An exhaust gas sensor may be positioned in an exhaust system of a vehicle to detect an air-fuel ratio of exhaust gas exiting from an internal combustion engine of the vehicle. Exhaust gas sensor readings may be used to control operation of the internal combustion engine to propel the vehicle.
The air-fuel ratio of exhaust gases may fluctuate from a desired ratio due to degradation in one or more components (e.g., a mass air flow (MAF) sensor, a fuel pump, etc.) or a change in fuel type. A lean fuel shift may result in a leaner than desired air-fuel ratio while a rich fuel shift may cause a richer than desired air-fuel ratio. Fuel shifts may affect engine control leading to an increase in emissions and/or reduced vehicle drivability. Accordingly, accurate determination of existing fuel shifts may reduce the likelihood of engine control degradation.
The inventors herein have recognized the above issues and identified an approach to at least partly address the above issues. In one embodiment, a method for an engine is provided for indicating a fuel shift based on a time delay of an exhaust gas sensor during an entry into and an exit out of deceleration fuel shut off (DFSO). Herein, fuel shifts during engine operation may be detected more accurately in a manner using existing hardware and fuel modulations that occur during DFSO events.
In one example, the exhaust gas sensor may be monitored for changes in air-fuel ratio, and a time delay response may be measured at each entry into and subsequent exit out of DFSO. As such, the exhaust gas sensor time delay response may be monitored during conditions that approximate lean-to-rich and rich-to-lean transitions to determine if fuel shifts are present without intrusive excursions. Herein, an entry time delay may be a duration from a start of the entry into DFSO to a first threshold change in air-fuel ratio. Further, an exit time delay may be a duration from a start of the exit out of DFSO to a second threshold change in air-fuel ratio. The entry time delay response may be compared with an expected entry time delay, and the exit time delay response may be compared to an expected exit time delay response. A rich fuel shift may be determined when the entry time delay is greater than the expected entry time delay, and the exit time delay is within a threshold of the expected exit delay. A lean fuel shift may be detected when the entry time delay is determined to be within a threshold of the expected entry time delay, and the exit time delay is greater than the expected exit time delay.
In this way, a non-intrusive and passive approach may be used to detect the presence of fuel shifts. Time delay responses from the exhaust gas sensor during entry into and exit out of DFSO events may provide a more robust signal that has less noise and higher fidelity. Thus, a more reliable diagnosis of existing fuel shifts may be made. Further, these fuel shifts may be mitigated by using closed loop feedback control and by tailoring engine control (e.g., throttle position, fuel injection amount and/or timing) responsive to the type of fuel shift.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.